What happened
On April 4, 2021, a private CH70 «Zenair» (registration HB-YKC) was performing a VFR flight from Bex to Bressaucourt. During the approach to runway 07, the pilot encountered moderate Bise winds with gusts reaching 15 knots. The pilot maintained an approach speed of approximately 55 to 60 MPH with 15 degrees of flaps extended.
As the aircraft crossed the runway threshold at a low altitude, the pilot attempted to flare the aircraft at roughly 1.5 to 2 meters above the surface. At an altitude of approximately 1 meter, the aircraft abruptly lost altitude and the main landing gear struck the runway. The impact was followed by a heavy strike to the nose gear, causing it to break away from the airframe. The propeller tips also made contact with the runway surface. The aircraft subsequently slid approximately 30 meters along the runway before coming to a halt. The pilot was uninjured.
The investigation
Investigators examined the aircraft's technical condition and the meteorological environment. No mechanical defects were found contributing to the incident. The investigation focused on the flight parameters and the impact of the wind conditions. The technical examination of the nose gear revealed that the strut had broken above the weld connecting it to the mounting plate, and the plate itself showed signs of being dented, suggesting the assembly had been subjected to forces exceeding its design limits prior to the break. The propeller's slipper clutch remained undamaged, though the engine gearbox required inspection following the propeller strike.
Findings
- The approach speed chosen by the pilot was too low given the prevailing wind conditions.
- The pilot operated with a very narrow margin (maximum 5 MPH) below the maximum flap-extended speed (VFE) of 60 MPH.
- The use of 15 degrees of flaps increased drag and the aircraft's susceptibility to turbulence.
- A sudden loss of lift, potentially caused by vertical wind shear or the aircraft entering the wind shadow of a nearby tree line, likely caused the sudden drop in altitude.
- The low landing mass of approximately 450 kg made the aircraft particularly sensitive to power reductions or wind disturbances.